1. Field of the Invention
This invention relates to an improved process for making liquid ferric sulfate. More particularly, the invention relates to a method that affords better control and efficiency in the digestion process for producing liquid ferric sulfate from finely-divided iron ore, sulfuric acid and water.
2. Description of the Prior Art
Ferric sulfate is a known product. It is commonly used in portable water and sewage treatment processes. These purification processes involve using ferric sulfate as a flocculent to remove suspended particles in the water.
Ferric sulfate has been produced from a variety of materials under different conditions. In the past, it has been commercially produced by reacting flue dust with sulfuric acid in a batch process. U.S. Pat. No. 2,252,332, issued to Plummer, describes such a process for making dry ferric sulfate.
As disclosed in Plummer, the flue dust was a waste product of a smelter and has less than 60% total iron content. The reaction between the flue dust and ferric sulfate was exothermic and drove off the water from the reaction. The resultant product was a solid mass, which usually took the form of fines, granules and large clumps.
Typically, a water treatment facility will purchase the dry ferric sulfate in bulk and store it in a silo until it is pneumatically transferred to the treatment tank. However, several problems are encountered in the use of dry ferric sulfate. One of the major problems is simply the transportation of the powder. It has a tendency to be hygroscopic and will frequently cake during storage.
Still another problem is that the dry ferric sulfate contains impurities from the initial feed stock of flue dust. These impurities are not removed during the sulfonation process so they form part of the solid mass that is produced. When the dry ferric sulfate is solubilized in the treatment water, these insoluble impurities precipitate as sludge. The total weight of the insoluble material could be as much as about 10% of the dry ferric sulfate. In addition to having to dispose of this sludge, the user also pays for material, which does not perform any useful function.
Consequently, there is still a need in the industry for a coagulant that can be easily transported through pipes and valves without clogging and which does not introduce extraneous material into the water treatment process.